1. Field of the Invention
The present invention relates to a structure for racking substrates, and more particularly, to a structure for racking substrates capable of distributing a load of a large-size mother substrate when a desired process is performed after the large-size mother substrate used to fabricate a liquid crystal display device has been loaded.
2. Discussion of the Related Art
In general, in a liquid crystal display device, a plurality of thin film transistor array substrates is formed on a large-size first mother substrate. A plurality of color filter substrates is formed on a large-size second mother substrate. Then, the first and second mother substrates are attached to each other, thereby forming a plurality of liquid crystal display panels at the same time. Thus, this process improves the yield of liquid crystal display panels.
Spacers are formed within the first and second mother substrates to precisely and uniformly maintain a cell-gap between the thin film transistor array substrates and the color filter substrates. Moreover, a liquid crystal layer is formed at the cell-gap.
The spacers can be formed by a dispersing method. In the dispersing method, particles such as a glass bead, a plastic bead, or the like having a certain diameter are dispersed with a uniform density on the first or second mother substrates, to thereby form the spacers. In such a dispersing method, the spacers may be formed at an effective display area since the particles such as a glass bead, a plastic bead, or the like are randomly dispersed on the first or second mother substrates.
The dispersing method has the following problems. Light transmitted within the effective display area is cut or diffused by the spacers. Moreover, leakage of light occurs since alignment of a liquid crystal layer may be crooked in an area where the spacers are located. Thus, an image quality of the liquid crystal display device is degraded. Degradations in image quality, such as blots, occur specially in large-size liquid crystal display devices because the spacers locally lump.
To solve such problems, a photolithography method for forming the spacers has been proposed. In the photolithography method, a photoresist film is applied on the first or second mother substrate. Ultraviolet light is selectively radiated on the photoresist film through a mask having a light cutting area and a transmitting area. Then, the photoresist film is developed. Accordingly, the photoresist film remains locally on the substrate. Thus, patterned spacers or column spacers are formed.
The patterned spacers or the column spacers formed by the photolithography method may overlap a black matrix formed at the second mother substrate. For this reason, deterioration in an aperture ratio and image quality of a liquid crystal display device may be prevented. In addition, a cell-gap between the first and second mother substrates is accurately maintained because the cell-gap between the first and second mother substrates may be controlled by a thickness of the photoresist film. Accordingly, the photolithography method is mainly used in fabricating a large-size liquid crystal display device.
The first and second mother substrates between which the spacers are formed are. attached to each other by a sealant. The sealant generally is formed along an outer edge of an effective display area of the first mother substrate or the second mother substrate.
The cell-gap between the first and second mother substrates is maintained by the spacers, and the first and second mother substrates are temporarily attached to each other by a sealant and then transported to hardening equipment. While the sealant hardens in the hardening equipment, the first and second mother substrates are attached to each other. Here, the temporarily attached first and second mother substrates are loaded by a robot-arm onto a racking structure provided in the hardening equipment.
To harden the sealant of the temporarily attached first and second mother substrates in the hardening equipment, annealing is performed at generally over 100° C. for about an hour. The hardening equipment includes the racking structure at which the temporarily attached first and second mother substrates are racked.
FIG. 1 is a plane view of a racking structure provided in hardening equipment according to related art. As shown in FIG. 1, the racking structure supports edges of both long sides of a substrate 1 through first and second side support bars 60 and 70. The racking structure supports the central portion of the substrate 1 through a central support bar 80.
The substrate 1 includes a large-size first mother substrate and a large-size second mother substrate. The large-size first mother substrate includes a plurality of thin film transistor array substrates. The large-size second mother substrate includes a plurality of color filter substrates. The large-size first and second mother substrates are separated from each other by spacers and are temporarily attached by a sealant. The substrate 1 is racked on the racking structure provided in the hardening equipment.
The substrate 1, including the temporarily-attached first and second mother substrates, increases in size and load in relation to the size of a liquid crystal display panel. However, in comparison, a thickness of the substrate 1 is very small due to a requirement for a thin liquid crystal display device.
Accordingly, if the first and second side support bars 60 and 70 support only edges of both long sides of the large-size substrate 1, any increase in size and load while maintaining a small thickness will cause the central portion of the substrate 1 to bend toward the ground. To support the central portion of the substrate 1 and thus prevent the center portion from bending toward the ground, the central support bar 80 supports the central portion of the substrate 1.
However, in the racking structure of the related art as described above, a load is concentrated on an area where an end of the central support bar 80 and the substrate 1 are in contact. Thus, the patterned spacers or the column spacers formed between the first and second mother substrates collapse or twist in the area where an end of the central support bar 80 and the substrate 1 are in contact.
When the patterned spacers or the column spacers collapse or twist as set forth above, a constant cell-gap may not be maintained between the first and second mother substrates. Thus, the collapse of the spacers causes degradations in image quality of a liquid crystal display device and particularly causes the occurrence of a black spot.